Incoprea Theory
Volume VII · 2026

Theory 01/Dermatology & Skin Barrier /Skin biophysics/3 min

The Barrier Fails at a Phase Transition

Barrier creams are formulated to add oil. The barrier may care about which phase the oil is in.

The claim

Skin barrier function collapses when the intercellular lipids undergo a phase transition rather than when the layer thins, so permeability should change sharply at a critical temperature and hydration, and emollients should work by shifting that transition.

01The evidence

  • Fine tuning of the skin barrier has been linked to a low-temperature lipid chain transition, with barrier properties changing at the transition rather than gradually with lipid amount.Journal of Investigative Dermatology
  • The phase behaviour of skin-barrier lipids has been characterised by combined experiment and simulation, which locates the transition and shows that permeability depends on the phase rather than only on composition.Biophysical Journal

02The tension

Barrier function is modelled as a diffusion problem through a lipid layer, with permeability proportional to thickness and lipid composition. That model explains slow changes and misses the abrupt ones, and formulation is guided by composition rather than by phase.

03The theory

The stratum corneum lipids form ordered lamellae. In the ordered phase, water diffuses slowly along a tortuous path; in the disordered phase, the path is shorter and permeability rises sharply.

Because a phase transition is cooperative, the change is abrupt at a critical temperature or hydration rather than gradual. That makes barrier failure a threshold phenomenon, and it predicts that two skins with the same lipid composition but different phase states will differ in permeability.

The prediction is that transepidermal water loss should change discontinuously with temperature at the transition, and that emollients which shift the transition temperature should improve barrier function without changing lipid quantity.

The formulation consequence is that phase behaviour, not oil content, should be the design target, and that a product which disorders the lipids can make the barrier worse while feeling better.

04What this is not

Composition-and-thickness barrier models

Those models make permeability a function of how much lipid is present. This makes it a function of which phase the lipid is in, which predicts abrupt changes that composition cannot explain.

05Predictions

  • P1Water loss should change discontinuously at the lipid transition temperature.
  • P2Emollients shifting the transition should improve barrier function at constant lipid content.
  • P3Skins matched on composition but differing in phase should differ in permeability.

06What would refute it

Permeability changing smoothly with composition and thickness, with no discontinuity at the transition, would leave the diffusion model adequate.

07What it would change

It would make phase behaviour the formulation target in dermatology.

08Evidence base

  1. Skin barrier fine tuning through low-temperature lipid chain transition — JIDhttps://www.sciencedirect.com/science/article/pii/S0022202X23024004
  2. Phase behaviour of skin-barrier lipids — Biophysical Journalhttps://www.sciencedirect.com/science/article/pii/S0006349524004776